ALSTHOM's published French Patent application No. 2550373 (equivalent to U.S. Pat. No. 4,543,272) describes an insulating method of this type, in which a tape is impregnated with a liquid epoxy resin and a benzyltrialkylammonium halide having an alkyl chain containing not more than 3 carbon atoms, in which the impregnated tape is dried at a temperature of not more than 135.degree. C., and is then impregnated with a varnish based on an isocyanate derivative prior to polymerizing the tape by heat treatment. Although the insulation obtained in this way is highly satisfactory and presents excellent electrical properties, research is nevertheless continuing in further improving the adhesion between the tape's porous mica paper and its glass felt or cloth or its film of plastic material, and also in increasing the flexibility of the resulting tape, in particular for insulating small diameter conductors.
The aim of the present invention is to provide insulation using a tape which is very flexible which is mechanically strong, which is not fragile, and which is easy to wind around conductors by machine.